Polyurethanes and polyisocyanurates are known generally in the art as being polyisocyanate-derived polymeric products. These products can be foamed or non-foamed, the former type receiving significant interest as an insulative and cushioning material in many and various industries during the past few years. The foamed polyurethanes are generally prepared by reacting the polyisocyanate with the polyol in the presence of a blowing agent (e.g. a normally gaseous fluorocarbon or carbon dioxide), the blowing agent expanding the reaction product during the reaction to produce a foamed or cellular structure. The polyurethane foams are characteristically and inherently non-heat-stable. Foamed polyisocyanurates are generally produced by reacting polyisocyanates in the presence of a trimerization catalyst and a blowing agent, the isocyanurate moiety imparting greater heat stability to the polymer. Where the polyisocyanate is a urethane prepolymer, or where it is trimerized in the presence of polyol, the resulting polymer contains urethane as well as isocyanurate linkages. The foamed products can be of high or low density, depending upon the amount of blowing agent used, and either rigid or flexible, depending upon the particular reactants used.
These foams can be generally referred to as poly(urethane-isocyanurates) or as urethane-modified polyisocyanurate foams. It is within the field of urethane-modified polyisocyanurate foams (sometimes referred to herein as polyisocyanurate foams) that the present invention resides.
Although the heat stability and structural strength of the semi-rigid and rigid polyisocyanurate foams have made them quite useful for many applications, such foams, particularly low density foams (e.g. 4 lbs./ft.sup.3.) have exhibited characteristically poor adhesion to substrates such as sheet steel containing contaminants such as oil, grease, or drawing compounds when foamed in situ. Consequently, it has always been necessary to remove such contaminants as oil or grease from the substrate surface before making the foam in situ in order to obtain suitable adhesion to such surface. Although more satisfactory results were obtained when forming high density foams (as opposed to low density foams) on oil-contaminated substrates, the expense and weight attendant with high-density foams are serious competitive disadvantages. Because completely removing oil and other such contaminants from substrate surfaces (e.g. metal) before making a foam on such substrates is highly impractical, and many times impossible, separate bonding agents or adhesives have been resorted to in order to anchor the foams to the substrates. Such approach is both time-consuming and expensive and often limits the structural strength of the structure to that possessed by the adhesive or other bonding agent. Consequently, there has been a need for a heat-stable semi-rigid or rigid low density foam which would readily adhere in a permanent manner to oil-contaminated substrates notwithstanding subjection of the structure to elevated temperatures, such as those used in baking a paint coating on the exposed substrate surface. The present invention provides such a foam.